1. Field of the Invention
The present invention relates generally to the bonding of gold or gold alloy wire to lead/tin solder pads. In more particular aspects, the invention relates to the compression bonding, either by thermocompression or thermosonic or ultrasonic bond of gold and gold alloy wires to lead/tin solder pads, and finds particular application in bonding wires to pads on semi-conductor chips.
2. Prior Art
In the production of semi-conductor chips, it is frequently necessary to bond various types of wire to attachment pads formed on the semi-conductor chips. The compositions of the pads as well as the wires and the techniques for bonding the wires to such pads have taken many different forms in the past. In some prior art configurations, the semi-conductor chips have been provided with aluminum or aluminum alloy pads to which wires must be bonded. Often gold wires were utilized and bonded to the pads by thermocompression bonding. An example of this type of bonding is disclosed in U.S. Pat. No. 3,091,849. In this particular patent, gold wires are thermocompression bonded to silicon surfaces of the underlying semi-conductor chip. Other methods of bonding have included solder bonding wherein the solder (such as lead tin solder) is used and melted to form a bond often to other pads also containing solder. This type of bonding is shown in U.S. Pat. No. 3,665,590.
It has also been found that it is not possible to obtain a good bond by normal reflow techniques between gold wire and lead/tin solder since the reflow of the lead/tin solder will dissolve the gold and not form a bond between the gold and the solder.